Mixing is a term applied to actions which reduce non-uniformities of materials in bulk. Such materials can be liquids, solids or gases, and the non-uniformities in such materials can occur in various properties, such as color, density, temperature, etc. The quality of mixing can be described by two characteristics--scale ("S") and intensity ("I"). The scale of a mixture is the average distance between the centers of maximum difference in a given property of the mixture, and intensity is the variation in a given property of the mixture.
The terms "S" and "I" are easily understood by the following illustration. Assume that in a shallow dish of white paint, a number of randomly dropped dollops of viscous black paint have been applied. Where all black paint within a dollop resides, the intensity "I" is 100%. In regions of white paint the intensity is 0%. The distance between the center of a black dollop and an adjacent white region is called the scale of mixing.
If the dish of paint were allowed to sit untouched, the demarkation between black and white would begin to blur as the peak or 100% intensity of the black paint diminishes, and the 0% intensity of the white paint rises. Finally, when enough time has passed, the intensity variation will asymptote to 0, and a uniformly gray paint mixture will result. Obviously, the smaller the scale of mixing, the more rapidly will the intensity variation asymptote to 0. Conversely, the higher the molecular diffusion, the larger the scale of mixing can be in achieving a given degree of mixedness for a given time period. Generally speaking, the higher the viscosity of a fluid, the lower will be its rate of molecular diffusion in any given solvent.
As design goals in producing the mixer of the present invention, it was the intent to reduce the scale of mixing rapidly, and thus promote a rapid drop in intensity.
The principles outlined above have particular application in the mixing of special polymers which are used in water treatment applications. These polymers are usually supplied having viscosities that can range from a few thousand centipoise to the order of one million centipoise. The polymers are generally diluted on site to save shipping costs and injected and mixed with the water to be treated as they cause particulates in water to agglomerate to form what is called "floc", which can then be filtered.
Obviously, such high viscosity polymers are difficult to dilute on site. The conventional mechanical mixing approach, consisting of a motor-driven paddle or blade in a tank, is clumsy, inefficient, an ineffective. Large lumps of undiluted polymer can circulate for hours or even days without being dissolved into solution. In addition, the very high shear rates associated with the tips of the blades can damage shear-sensitive polymers by breaking up the long chain polymers and reduce the flocculation efficiency. This is particularly true for emulsion polymers.
Even though such special polymers used in water treatment applications are introduced to, for example, ten times their own volume of water, the mixture will have a much higher viscosity than the original, undiluted matter--often ten to 50 times higher. Typical dilution ratios are 200 to one. In examining this problem, it became obvious that an appropriate mixing system would be one which would break up the water/polymer elements into very small components so as to achieve a minimum scale of mixing. It was also recognized that the appropriate mixing system should be one which could provide for controlled shearing to cause a smearing of the elements together. This aids in molecular diffusion by increasing the interfacial area and by reducing interfacial thickness. It was obviously a design goal to accomplish this result in the shortest amount of time, preferably in the order of one second or less.
It is thus an object of the present invention to achieve the above-recited results inexpensively and without undue complexity.